Blue Moon

And then there suddenly appeared before me? It’s a common misconception (but one that’s generally accepted) that a Blue Moon is the second full moon in a single month. But truly, this is not the case. In reality, a Blue Moon is the 3rd full moon in a season when that season has 4 full moons instead of the usual 3, seasons being specifically marked by equal 3 month intervals between solstices and equinoxes, rather than just calendar quarters. Scientifically speaking, an average lunar cycle is 29.53 days long and one solar year has approximately 365.25 days. If we divide 365.25 days by 29.53 days we come out with 12.37 lunations, which doesn’t quite fit with our tidy Gregorian Calendar of precisely 12 months in a year (the word “month” being derived from the word “moon” somewhere or other). Thus, each calendar year will be approximately 11 days longer than the number of days in 12 lunar cycles. While we throw in a Leap Year here and there, the extra days continue to accumulate and so, every two or three years (7 times in the 19-year-long Metonic Cycle), there will be an extra full moon falling within the 12 month calendar. Since the year is divided into four seasons, that extra moon will necessarily fall into one of them, creating a season of 4 moons rather than 3. “Now”, one might ask, “why is it the 3rd moon and not the last moon in that season considered to be the extra or “Blue” moon? And why the term Blue?” (I should add that if you’re not asking those questions, there’s not much point in reading the rest of this.) The answer to both begins with the early Christian church defining Easter as the first Sunday after the first full moon following the spring equinox (a mouthful, I know, and not even an original one if you take Passover into consideration). Therefore, it became incredibly important to correctly predict the equinox, especially when there was a full moon close to it, as an incorrect prediction would lead to an incorrect assignation of date and the damnation of entire villages if Lent was ended early (this was not a kind and generous God in those days). We now know that the spring equinox (the day when day and night are of equal length and the sun rises exactly in the East and sets exactly in the West) is going to occur on or around March 21st and a remarkable amount of our modern mathematics and astronomy was derived from this early quest to accurately predict that date. And so we get to the origins of the term “Blue Moon”: with the God referred to not being one to take Lenten vows lightly, clergymen needed to tell their flock which moon was the one signifying the coming of Easter and warn them in the case of a false full moon, which would have them accidentally ending Lent a month early---this false full moon was then named a “Belewe” (translating to “Betrayer”) Moon, and you can guess what happened from there. The particular Blue Moon picture above occurred on August 20th, 2013 and the next of its kind won’t come around til May 21st, 2016. Of definite note is the fact that the next time a Blue Moon falls on New Year’s Eve will be Dec. 31st, 2028, which will end one Metonic Cycle. It’ll also be a total lunar eclipse. Get ready.